Intermittent Fasting: Does It Actually Work for Weight Loss?

What Is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It doesn't specify which foods to eat but rather when to eat them. It has become one of the world's most popular health and fitness trends, with multiple clinical studies examining its effects on weight, metabolic health and longevity.

Popular IF Protocols

Protocol	Eating window	Fasting period	Difficulty
16:8 (Leangains)	8 hours	16 hours	Low–Medium
18:6	6 hours	18 hours	Medium
5:2 Diet	Normal × 5 days	500 kcal × 2 days	Medium
OMAD	1 hour	23 hours	High
Alternate Day Fasting	Every other day	24 hours	Very high

The 16:8 protocol (e.g., eating between 12pm and 8pm, fasting from 8pm to 12pm next day) is by far the most popular due to its simplicity and relatively low disruption to daily life.

Does IF Work Better Than Regular Dieting?

The honest answer from the research: intermittent fasting is about as effective as continuous calorie restriction for weight loss — not better, not worse, when total caloric intake is equated.

A landmark 2020 NEJM study comparing IF to continuous restriction found no significant difference in weight loss, fat mass or metabolic markers when calories were matched. IF works primarily because it reduces the total time available for eating, which for many people naturally reduces caloric intake.

However, IF has real advantages for some people:

Simplifies meal planning (fewer meals to think about)
Reduces the frequency of food decisions, lowering decision fatigue
Some people find it easier to skip breakfast than to eat smaller portions all day
May improve insulin sensitivity in some populations

Who Should Avoid Intermittent Fasting?

Pregnant or breastfeeding women
People with a history of eating disorders
Type 1 diabetics or those on insulin medication
Children and teenagers
People who are underweight

Anyone with a medical condition should consult their doctor before starting IF.

Frequently Asked Questions

Does coffee break a fast?Black coffee (no milk, sugar or cream) does not meaningfully break a fast. It contains minimal calories and may actually enhance fat oxidation and appetite suppression during the fasting window.

Will I lose muscle with intermittent fasting?No more than with any other form of caloric restriction, provided protein intake is adequate (1.6+ g/kg/day) and resistance training is maintained. In fact, some research suggests IF may be slightly better at preserving lean mass than equivalent continuous restriction.

Can I exercise during the fasting period?Yes. Fasted training (exercising before breaking the fast) is practised by many and is safe for most people. It may increase fat oxidation during the workout, though it doesn't necessarily burn more fat overall. If performance suffers, consider training just after your first meal.

Related Calculators

Sources

WHO CDC